Distribution of GABAC-like responses among acutely dissociated rat retinal neurons
GABAergic responses of acutely dissociated rat retinal neurons, including both bipolar cells (BCs) and other, morphologically round cells (RCs), were assayed with the fluorescent (FL), voltage-sensitive probe oxonol DiBaC4(5). Using intensified video microscopy and simultaneous recording, GABA responses were identified in one-third of cells in a typical microscope field; of these 85% hyperpolarized (0.05–0.3 log unit FL decreases) while the remainder depolarized (0.05–0.2 log unit FL increases). GABA-sensitive cells were also TACA-sensitive (trans-4-Aminocrotonic acid), and these ligands appeared interchangeable in ability to evoke responses. In RCs, an asymmetric co-responsive pattern was observed between GABA- and muscimol-evoked events. Muscimol-sensitive RCs responded well to GABA, but not all GABA-sensitive RCs responded to muscimol. In GABA-sensitive BCs, muscimol responses were typically weak or absent. Few BCs or RCs responded to CACA (cis-4-Aminocrotonic acid). Bicuculline-resistant GABA responses occurred in [similar]80% of GABA-responsive RCs and BCs. Both bicuculline-sensitive (GABAA-like) and bicuculline-insensitive (GABAC-like) responses were resistant to picrotoxin. Although a small minority of GABA-sensitive cells hyperpolarized in response to R(+)baclofen, bicuculline-insensitive responses were not antagonized by 2-hydroxysaclofen, and were abolished in low [Cl−]o. Results suggested (1) that bicuculline-insensitive, Cl−-dependent, GABAC-like responses were broadly distributed and predominant among dissociated rat retinal neurons; (2) that muscimol was a particularly weak agonist for rat retinal BCs; and (3) that oxonol was a sensitive probe for retinal GABA responses.(Received October 27 1997)
(Accepted July 2 1998)
Key Words: Retina; Bipolar cell; GABA; Oxonol; Rat.
c1 Correspondence and reprint requests to: Ralph Nelson, Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 36 Room 2C02, 36 Convent Dr. MSC 4066, Bethesda, MD 20892-4066, USA.
p1 Present address of Yong-Xin Li: Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125, USA.